• Josh Bleecher Snyder's avatar
    cmd/compile: eliminate dead code in if statements after typechecking · dffe5ac9
    Josh Bleecher Snyder authored
    This is a more thorough and cleaner fix
    than doing dead code elimination separately
    during inlining, escape analysis, and export.
    
    Unfortunately, it does add another full walk of the AST.
    The performance impact is very small, but not non-zero.
    
    If a label or goto is present in the dead code, it is not eliminated.
    This restriction can be removed once label/goto checking occurs
    much earlier in the compiler. In practice, it probably doesn't
    matter much.
    
    Updates #19699
    Fixes #19705
    
    name       old alloc/op      new alloc/op      delta
    Template        39.2MB ± 0%       39.3MB ± 0%  +0.28%  (p=0.008 n=5+5)
    Unicode         29.8MB ± 0%       29.8MB ± 0%    ~     (p=1.000 n=5+5)
    GoTypes          113MB ± 0%        113MB ± 0%  -0.55%  (p=0.008 n=5+5)
    SSA             1.25GB ± 0%       1.25GB ± 0%  +0.02%  (p=0.008 n=5+5)
    Flate           25.3MB ± 0%       25.3MB ± 0%  -0.24%  (p=0.032 n=5+5)
    GoParser        31.7MB ± 0%       31.8MB ± 0%  +0.31%  (p=0.008 n=5+5)
    Reflect         78.2MB ± 0%       78.3MB ± 0%    ~     (p=0.421 n=5+5)
    Tar             26.6MB ± 0%       26.7MB ± 0%  +0.21%  (p=0.008 n=5+5)
    XML             42.2MB ± 0%       42.2MB ± 0%    ~     (p=0.056 n=5+5)
    
    name       old allocs/op     new allocs/op     delta
    Template          385k ± 0%         387k ± 0%  +0.51%  (p=0.016 n=5+5)
    Unicode           321k ± 0%         321k ± 0%    ~     (p=1.000 n=5+5)
    GoTypes          1.14M ± 0%        1.14M ± 0%    ~     (p=1.000 n=5+5)
    SSA              9.71M ± 0%        9.72M ± 0%  +0.10%  (p=0.008 n=5+5)
    Flate             234k ± 1%         234k ± 1%    ~     (p=0.690 n=5+5)
    GoParser          315k ± 0%         317k ± 0%  +0.71%  (p=0.008 n=5+5)
    Reflect           980k ± 0%         983k ± 0%  +0.30%  (p=0.032 n=5+5)
    Tar               251k ± 0%         252k ± 0%  +0.55%  (p=0.016 n=5+5)
    XML               392k ± 0%         393k ± 0%  +0.30%  (p=0.008 n=5+5)
    
    Change-Id: Ia10ff4bbf5c6eae782582cc9cbc9785494d4fb83
    Reviewed-on: https://go-review.googlesource.com/38773
    Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
    Reviewed-by: 's avatarMatthew Dempsky <mdempsky@google.com>
    dffe5ac9
issue19699.go 191 Bytes